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1995 Blazer 4.3 Vortec question

MrSluggo MrSluggo
User | Posts: 75 | Joined: 10/11
Posted: 10/19/11
04:53 PM

Hello everyone, and thanks in advance for any advice you can give me.

My 1995 Blazer just quit running about 1 yr ago, I was driving and it started to run rough and died out. I tried to start it and it backfired and started back wheel well on fire. Anyway, after I got it home it would start and run for about 20 min or so, and stall out every time, and then would start again after about an hour.

I thought it was running rich because plugs were wet on all 6 cyl. but am now starting to think it may be oil. btw have I have replaced coil, control module, checked wires, cap and rotor, and injector assembly was done a few years ago, and there is no washing on inside of plenum, and I'm sure system has no leaks. Compression is good, vacuum is only at 11.5 inches but I moved to Denver 1 yr ago and not sure what Vac should be here. I have scanned with actron obd 2 scanner and get no codes, and no cel comes on.

Sorry so long so i'll cut this short with one last thing. Today I noticed oil coming from exhaust manifold flange on drivers side, and am sure it's not coming from anywhere else on engine. I'm thinking inake manifold gasket internal leak ?

Thanks again for any help you can give me.  

waynep7122 waynep7122
Addict | Posts: 4551 | Joined: 08/09
Posted: 10/19/11
06:52 PM

lets start with ...

Spark or no spark...  from the coil wire end when the engine is being cranked????

Spark or no spark from the end of one or more of the spark plug wires while the engine is being cranked????

can you hear the fuel pump run for 2 seconds when you turn on the key????

does the check engine light come on when you turn the key to the ON position...

what model scan tool do you use.. not all will work with the 94/95 model years as they are actually OBD1.5...  where is uses the obd2 connector but obd1 type of codes and data stream..

if you post the brand and model of the scan tool.. i will take a look through the various owners manuals i have scattered for some and see if i can help you with them...  

MrSluggo MrSluggo
User | Posts: 75 | Joined: 10/11
Posted: 10/19/11
07:19 PM

Model number for scanner is actron II autoscanner

MrSluggo MrSluggo
User | Posts: 75 | Joined: 10/11
Posted: 10/19/11
07:39 PM

I wrote a reply earlier but it does not seem to be showing up so i'll reply again.

It does have spark and runs, but spark seems to be a bit weak because of orange color, but spark does jump over an inch from spark plug end of wires.

Fuel pump seems to be working fine, and when I checked it in the past I had a reading of 60

Check engine light is not working, but I do get codes from scanner when I unplug map, tps etc....

Compression check reading was about 165 psi per cyl. with only 1 or 2 cyl being off maybe 3 to 4 psi of highest reading.

I tried a cyl balance test but really couldn't get the plugs off when running so it was hard to tell differences in rpm, but this seems to be affecting all cyl. anyways.

Vac reading is 11.5 steady reading (no jumping)which seems low to me, but I'm in Denver and I know vac goes down with higher elevation, but not sure what it should be here. Vac drops down to zero when throttle is snapped open, but comes back to normal fast with no delay so I don't believe it's exhaust restriction.  

waynep7122 waynep7122
Addict | Posts: 4551 | Joined: 08/09
Posted: 10/20/11
12:19 AM

have you examined the distributer..   they have failed.    please preset the engine to the rotor pointing at the proper position in the cap and the little number 6 in the top of the distributer housing ...  then line up the crank timing marks..  

its its out of sync.. the engine will backfire and buck and spit. if it runs at all..

checked that the cam sensor in the distributer has not failed...    

did you verify the ground wires????

more tomorrow..ZZZZZZZZZZZZ!!!!  

MrSluggo MrSluggo
User | Posts: 75 | Joined: 10/11
Posted: 10/20/11
09:09 AM

I put a junkyard dist. in some time back, and it made no difference, but I guess that could have been bad also, but it seemed to be good with very little shaft movement. I have read that the gear on dist. on this model can go bad though so I am going to check that out.

I have put a timing light on motor and couldn't see the timing mark, but not sure if I need to unplug something or not ? I had two haynes manuals for this truck at one time and now I can't find them Frown

I have the flat top dist. cap, and I don't believe there is a cam sensor in there from what I remember. I have checked the crank sensor and that was good.

When running, and it is missing bad, I don't get any misfire codes, but when I unplugged egr and ran motor I did get a misfire code, not sure what to make of that.

Thanks for the help!!


MrSluggo MrSluggo
User | Posts: 75 | Joined: 10/11
Posted: 10/20/11
09:51 AM

I forgot to add that the engine is running now and not shutting down after twenty minutes, But it is still running bad but not backfiring, just missing. And I should add that all 6 spark plugs are oil soaked, actually wet.  

waynep7122 waynep7122
Addict | Posts: 4551 | Joined: 08/09
Posted: 10/20/11
04:47 PM

well ... oil well..

i would like to know... is it truly OIL on the spark plugs.. or are they wet with fuel????

can you stick a fuel pressure gauge back on the fuel rail test port....    monitor fuel pressure after shut down..

does it hold pressure when shut down???

why.. there is a fuel pressure regulator on the front of the fuel injector block that can leak...   right into the open intake ports..

there have also been cases of cuts and rub through damage to the fuel tubes... causing leaks...  the bracket has sharp edges where it was die cut.. i wish they would tumble deburr them.. but its kinda up to you to hit it with the file or wire wheel on the bench grinder..

you could also have a leaking intake manifold gasket...   where it is pulling oil and vapors from the crank case...

this is not impossible to find. if you disconnect the pcv and block it.. then see if there is still vacuum being built up in the crank case through the breather hose.....

you could also have damaged cylinder walls or pistons and rings that are damaged...

have you done a compression test???

another thing...

did i post a voltage drop test????    as the ECM is ONLY grounded to the engine.. if the engine is not properly grounded not just to the battery. but also the battery to the body and the engine to the body.. you will have different voltages between parts..

take a digital volt meter...

set it to 20 volts DC scale...

start the engine and turn on the headlights..

1. test between the positive and the negative battery posts.  14.1 to 14.8 volts is expected.

2. test between the negative battery post and the engine block. 0.04 volts is expected..

3. test between the negative battery post and the body... 0.02 volts is expected..

4. test between the Engine block and the body..  0.02 volts is expected.

if you get 0.00 on the last 3 tests.. change the meter setting to 2 volts DC scale.. and retest.. the last 3...

this test takes about 2 minutes...

post your results by test number..

if you get more than the 0.04 or 0.02 volts on the display...

you have a bad ground between those parts..

why do this test....   bad grounds will stop any new car in its tracks...

why... electrons flow from Negative to positive...  if you loose a ground.. or it becomes intermittent..  you won't have any power for that circuit...

oil drain back holes in the rocker arm areas clogged... and the PCV in the valve cover pulling oil directly into the intake...  

MrSluggo MrSluggo
User | Posts: 75 | Joined: 10/11
Posted: 10/20/11
10:06 PM

Hello Wayne,

I still can't find my manual and I checked tdc with rotor and moved it to #1 cyl Frown I was wrong.
It was set right before I moved it now it's 180 off, the posts inside the cap are different, I wish they would number the cap, oh well. Not a big deal I can move it back easy enough.

When I was doing the dist. I could feel ground on back of motor, but could not look at connection or see where it hooked to firewall, so I'm going to do the voltage drop tests you suggested.

I checked batt. ground to engine and cleaned it up.

Charging system is good in the 14 plus volt
range. Comp. tested all cyl. and they all tested at 165 psi +/- 2 to 3 psi, but since there is oil in the cylinders that would be a wet test, sigh. Think I might need to do a leakdown test to rule out the rings.

I have checked the pcv valve, and it rattled, and when I plugged it the rpms dropped some, so I think that's ok.

One more thing, could a leak in the intake manifold gasket get oil to all cyl. ?

Have a good night, and I look forward to hearing your thoughts on the intake manifold gasket affecting all cyl.



waynep7122 waynep7122
Addict | Posts: 4551 | Joined: 08/09
Posted: 10/21/11
01:33 AM

this is the Vortec distributer.. notice the cam sensor???

can you see a arrow just inside the lip of the housing at about the 7 o clock position.. that is the direction the tip of the rotor is supposed to point in when you have the number one piston at TDC on the compression stroke..  and the Crank set to TDC...
some have just a 6   some have a 6 and then an 8 in another location around the lip..

if it backfires.. or just plain old runs bad.. this distributer/cam sensor timing in relation to the crank sensor is probably off.. since this is a central port fuel injected motor.. and you have replaced the spider.. you probably now have an SCPI or a sequential port fuel injected motor.. as most of the replacement spiders move the injector down to the ends of the nozzles.. rather than having poppets at the end that the pressure has to build up with the injector pulse width to get them to spray..

there is a setting done with advanced scan tool for crank sensor cam sensor offset degrees... that will set a trouble code..

compression looks good.. you don't need to do the leak down test..  you won't find anything...

oil in the intake... getting into all the cylinders???  i have changed a bunch of the lower intake manifolds.. i was more worried about getting everything perfectly clean...  i used bath towels over the open lifter valley. tucked in between the tops of the push rods.. so i could scrape away with my 5 way painters tool that i keep razor sharp with a diamond file.. by running the sharp edge side to side down the length of the file.. so its sharp and flat..  i drag it across the flat side just once.. takes the burr off..   allows me to scrape aluminum machined without digging in ..

does this engine have a LONG oil filler tube.. or can you take the oil filler cap off ... look down in the valve cover with the engine running.    see if there is more than an inch of oil around the bottom of the springs..

i seem to recall that this version has a removable tuning port so you can see into the inside... perhaps i am wrong..

there is one thing.. that can cause the spark plugs to all be fouled...  clogged/blocked exhaust system..

do you have a vacuum gauge?????   can you find an manifold vacuum port..   raise the engine speed slowly.. does the manifold vacuum stay the same or increase..  

if the exhaust is blocked.. the intake manifold vacuum will reduce with engine speed..   you can double check if the vacuum drops.. by removing an oxygen sensor...  if the vacuum returns as you speed the engine up.. you have a blocked exhaust. .

cats can clog..   the exhaust pipes are double wall..  the inner wall can collapse leaving the outer wall intact.. the internal components in the muffler can once in a while cause a restriction..

i have used the shop vacuum to test for flow..   with the head pipes disconnected from the manifolds.. tennis balls to block one side then the other..   cold exhaust..   one of the other guys thought that was a good idea.. but did not understand..  he hooked the vacuum to a running motor and melted the hose..  i am glad they sell those individually..  

MrSluggo MrSluggo
User | Posts: 75 | Joined: 10/11
Posted: 10/21/11
11:36 AM

I do have a tuning valve and have looked inside while having my son turn the key and I did not see or hear any leaks on either side.

I have checked the vac and get a reading of 11.5 steady,I know it's low but i'm in Denver 5,600 or so feet so not sure if this is really low a reading. When I snap the throttle the vac goes to zero but comes back fast, and when I increase rpm it does not drop vac. so I don't believe exhaust is restricted.

I have tried a different cam sensor but it was junkyard cam sensor so I'm not sure if it was good. I don't know how to test for this being bad, and I'm  not getting a code for it, but I'm using obd II on a obd 1.5 system so not sure if I would get a code. You think it may be a good idea to put a new cam sensor in ?

I'm leaning towards valve seals, intake manifold gasket, which would make sense with vac. being a bit low,and or piston rings being bad and that's why I thought a leakdown test could atleast rule rings out if that's not the problem.



waynep7122 waynep7122
Addict | Posts: 4551 | Joined: 08/09
Posted: 10/21/11
11:46 AM

with a bad cam sensor.. the engine would probably NOT start at all..

were you able to examine the distributer picture above.. the little mark is just barely visible.

can you read any live data stream with your scan tool???


waynep7122 waynep7122
Addict | Posts: 4551 | Joined: 08/09
Posted: 10/21/11
11:47 AM

can you go over the exact troubles now...  

MrSluggo MrSluggo
User | Posts: 75 | Joined: 10/11
Posted: 10/21/11
12:57 PM

It's missing which I believe is random. It used to run only 20 min, but now it keeps running but just runs bad. Can see oil coming from drivers side exhaust flange, and all plugs have oil and or mix of gas and oil. Think it's more oil because get some blue smoke out of exhaust and when I take a flame to pulled spark plug it won't burn at all.

Vac. 11.5 steady,does not drop when rpms are increased, and vac comes back fast after throttle snapped open. Do you still think it could still be restricted ? Hate to get into exhaust if don't have to since I'm from Minnesota and it's rusted pretty good. Charging system good, compression check 165 psi per cyl., but if oil is in cylinders this would be a wet test and won't tell me if rings are bad.

Scanner gives me codes when I unplug sensors otherwise I have no codes. I would think it should show a misfire code but it doesn't.
I don't think I can read live data stream, but can get a review when a code is set with some freeze data on it. Scanner is actron obd II autoscanner #CP9175


MrSluggo MrSluggo
User | Posts: 75 | Joined: 10/11
Posted: 10/21/11
01:05 PM

Wanted to say that I'm in Denver now not Minnesota so you don't get confused with vac reading.  

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